Inhibition of ATP-activated current by zinc in dorsal root ganglion neurones of bullfrog.
1. The effect of Zn2+ on ATP-activated current was studied in bullfrog dorsal root ganglion (DRG) neurones using the whole-cell patch-clamp technique. 2. Zn2+ (2-800 microM) inhibited current activated by submaximal concentrations of ATP. The Zn2+ concentration that produced 50% inhibition (IC50) of current activated by 2.5 microM ATP was 61 +/- 9.8 microM. When ATP concentrations were adjusted to account for chelation of Zn2+, the IC50 of Zn2+ was 86 +/- 18 microM. 3. The inhibitory action of Zn2+ on ATP-gated channels did not appear to be due to a decrease in the concentration of one or more species of ATP. 4. Zn2+ inhibition of ATP-activated current was independent of membrane potential between -80 and +40 mV, and did not involve a shift in the reversal potential of the current. 5. Zn2+ (100 microM) shifted the ATP concentration-response curve to the right in a parallel manner, increasing the EC50 for ATP from 2.5 +/- 0.5 microM to 5.5 +/- 0.4 microM. 6. Zn2+ decreased the time constant of deactivation of ATP-gated ion channels without affecting the time constant of activation or desensitization. 7. Dithiothreitol (DTT) reversed Zn2+ inhibition of ATP-activated current. 8. 2-Methylthio ATP, alpha,beta-methylene ATP and ADP activated current with EC50 values of 2.4 +/- 0.3. 50.1 +/- 5.8 and 303.1 +/- 53.9 microM, respectively. Adenosine, AMP or beta,gamma-methylene ATP did not evoke detectable current. 9. Reactive Blue 2 and pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid inhibited ATP-activated current. 10. The results suggest that Zn2+ can inhibit P2X purinoceptor function by decreasing the affinity of the binding site for ATP. These observations provide the first evidence for this action of Zn2+ on a neurotransmitter-gated ion channel. Furthermore, the receptor-channel in these neurones appears to be a novel member of the P2X purinoceptor class.
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Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892-8115, USA. cli@niaaa.nih.gov
Peoples
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D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000502:physiology*; D000818:Animals; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011892:Rana catesbeiana; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000502:physiology*; D013126:Spinal Nerve Roots / Q000166:cytology / Q000502:physiology*; D015032:Zinc / Q000494:pharmacology / Q000502:physiology*
D007473:Ion Channels; D018048:Receptors, Purinergic P2; D000255:Adenosine Triphosphate; D015032:Zinc